The National Weather Service (NWS) issued a flash flood emergency warning around noon Wednesday for Boerne and Kendall County, where footage posted online shows road closures, rivers breaching their banks and emergency crews launching rescue boats.

"THIS IS A PARTICULARLY DANGEROUS SITUATION!" the NWS said in a tweet.

"Move to high ground if you are near Cibolo Creek or smaller tributaries. Turn Around, Don't Drown if you encounter a flooded roadway!" Sign up The NWS alert - an enhanced type of flash flood warning - expires at 8:15 p.m. It affects some 26,000 residents of the San Antonio exurb.